Formation of Biogenic Amines and Associated Biochemical and Microbial Attributes of Whole Sutchi Catfish (Pangasianodon hypophthalmus) during Iced Storage

Sutchi catfish (Pangasianodon hypophthalmus) is a highly preferred farmed species that is produced in huge quantities. Meat from ice-stored (4 ± 2°C) whole Sutchi catfish was evaluated for formation of biogenic amines, such as putrescine, cadaverine, histamine (HIM), agmatine, tyramine, spermine, and spermidine, and compared with biochemical, microbial, and sensory attributes during 22 days. Analysis of content of biogenic amines in the meat was carried out by liquid chromatography with tandem mass spectrometry using a without derivatization method. Three amines, namely, tyramine, spermidine, and spermine, were only present on 0^th day of storage. Presence of cadaverine was noticed from 9^th day onwards, where the aerobic plate count (APC) reached 4.85 log CFU/g. Putrescine was detected on the 22^nd day of storage, where the APC crossed 7 log CFU/g. HIM was detected in lower quantities from 3^rd day onwards. A shelf life of 15 days was determined based on sensory and microbiological evaluation. Although the samples were biochemically acceptable throughout the storage period, APC exceeded the limit on day 19, and the gradual increase of H₂S-producing bacteria, Brochothrix thermosphacta, Aeromonas, and Enterobacteriaceae, was observed during storage.     

Colouring ornamental fish (Cyprinus carpio and Carassius auratus) with microalgal biomass

Koi carp and goldfish value increases with intensity of skin colour, which is an important quality criterion. Fish cannot fully synthesize their own carotenoid colourings and these must therefore be included in their diet. Two trials were undertaken to investigate skin colour enhancement in ornamental species (i.e. three chromatic varieties of koi carp (Cyprinus carpio), namely Kawari (red), Showa (black and red) and Bekko (black and white) and goldfish (Carassius auratus)) by feeding a dietary carotenoid supplement of freshwater microalgal biomass [Chlorella vulgaris, Haematococcus pluvialis, and also the cyanobacterium Arthrospira maxima (Spirulina)], using a diet containing synthetic astaxanthin and a control diet with no colouring added for comparison. In the first trial, five homogeneous duplicate groups of 25 juvenile koi carp (C. carpio) (initial mean body weight 24.6 ± 0.7 g) were fed, for 10 weeks, one of the four diets containing 80 mg colouring/kg diet. In the second trial, this procedure was repeated for five homogeneous duplicate groups of 25 goldfish (C. auratus) (initial mean body weight of 0.9 ± 0.1 g). Initial and final samples of skin along the dorsal fin were withdrawn, from five fish per group, for subsequent analysis of total carotenoid content (spectrophotometric analysis), and red hue (colorimetric analysis, CIE (1976) L* a* b* colour system). Growth and feed efficiency were not significantly different between groups administered by the various dietary treatments. In both trials, dietary carotenoid supplementation increased total skin carotenoid content. The more efficient colouring for koi carps was found to be C. vulgaris biomass, providing both maximum total carotenoid deposition and red hue for the three chromatic koi carp varieties studied, and particularly for the kawari variety. For goldfish the best colouring obtained, as ascertained by total carotenoid content, was also achieved using C. vulgaris biomass, and red hue was maximum when using H. pluvialis biomass.     

Changes in Biogenic Amines and Bacteria of Tiger-Toothed Croaker (Otolithes ruber) during Ice Storage

Changes in the content of biogenic amines (BA; e.g., putrescine, tyramine, and histamine) and the mesophilic and psychrotrophic bacterial counts of tiger-tooth croaker (Otolithes ruber) were monitored during ice storage for 18 days. BA and bacterial loads gradually increased (p < 0.05) with storage time. On the first day of storage, no amines were detected, and no histamine was detected up to 6 days. The best linear regressions between BA and bacterial counts were found between putrescine and psychrotrophic bacteria. Furthermore, it was found that psychrotrophs were the dominant microorganisms during storage and showed significant (p < 0.05) differences with storage time. The initial concentration of putrescine was 1.27 μg g^?1 and reached 18.8 μg g^?1 when the psychrotrophic bacterial load was over 10⁸ CFU g^?1. The results suggest that the level of putrescine is a suitable indicator of freshness for O. ruber, and the shelf life of O. ruber stored in ice as determined by BA content and microbiological data was 10 days.     

Cage colour and post-harvest K+ concentration affect skin colour of Australian snapper Pagrus auratus (Bloch & Schneider, 1801)

In an attempt to improve post‐harvest skin colour in cultured Australian snapper Pagrus auratus, a two‐factor experiment was carried out to investigate the effects of a short‐term change in cage colour before harvest, followed by immersion in K⁺‐enriched solutions of different concentrations. Snapper supplemented with 39 mg unesterified astaxanthin kg^?1 for 50 days were transferred to black (for 1 day) or white cages (for 1 or 7 days) before euthanasia by immersing fish in seawater ice slurries supplemented with 0, 150, 300, 450 or 600 mmol L^?1 K⁺ for 1 h. Each treatment was replicated with five snapper (mean weight=838 g) held individually within 0.2 m³ cages. L^*, a^* and b^* skin colour values of all fish were measured after removal from K⁺ solutions at 0, 3, 6, 12, 24 and 48 h. After immersion in K⁺ solutions, fish were stored on ice. Both cage colour and K⁺ concentration significantly affected post‐harvest skin colour (P<0.05), and there was no interaction between these factors at any of the measurement times (P>0.05). Conditioning dark‐coloured snapper in white surroundings for 1 day was sufficient to significantly improve skin lightness (L^*) after death. Although there was no difference between skin lightness values for fish held for either 1 or 7 days in white cages at measurement times up to 12 h, fish held in white cages for 7 days had significantly higher L^* values (i.e. they were lighter) after 24 and 48 h of storage on ice than those held only in white cages for 1 day. K⁺ treatment also affected (improved) skin lightness post harvest although not until 24 and 48 h after removal of fish from solutions. Before this time, K⁺ treatment had no effect on skin lightness. Snapper killed by seawater ice slurry darkened (lower L^*) markedly during the first 3 h of storage in contrast with all K⁺ treatments that prevented darkening. After 24 and 48 h of storage on ice, fish exposed to 450 and 600 mmol L^?1 K⁺ were significantly lighter than fish from seawater ice slurries. In addition, skin redness (a^*) and yellowness (b^*) were strongly dependent on K⁺ concentration. The initial decline in response to K⁺ was overcome by a return of a^* and b^* values with time, most likely instigated by a redispersal of erythrosomes in skin erythrophores. Fish killed with 0 mmol L^?1 K⁺ maintained the highest a^* and b^* values after death, but were associated with darker (lower L^*) skin colouration. It is concluded that a combination of conditioning snapper in white surroundings for 1 day before harvest, followed by immersion in seawater ice slurries supplemented with 300–450 mmol L^?1 K⁺ improves skin pigmentation after >24 h of storage on ice.     

Environmental control of skin colour in the red porgy, Pagrus pagrus

Fish display sophisticated skin chromatic properties that are of considerable ecological, physiological and behavioural importance. The aim of study was to investigate the role of important physical parameters (background colour, lighting spectrum, light intensity and water temperature) on skin colour to gain better knowledge of the environmental factors that regulate pigmentation in cultured red porgy, Pagrus pagrus . All tested physical parameters had a significant effect on skin lightness, especially in the dorsal body area; low light intensity, blue spectrum, a water temperature of 19 °C and a white background significantly increased skin lightness. This effect was mediated through changes in melanophore motility and/or skin melanin concentration. None of the examined factors affected skin hue while a significant decrease in skin entire colour index (a combination of hue and chroma) was found only in white background-adapted fish. It is concluded that all tested physical factors are important regulators of skin lightness.     

Determination of growth,colour and other traits in F1 hybrid of Amphiprion percula (male) × A. ocellaris (female)

This study reported the traits values such as colour, feed conversion ratio (FCR), specific growth rate (SGR) and fluorescence capacity of F₁ hybrids of Amphiprion percula (male) and A. ocellaris (female). The hybrids exhibited significant variation in FCR (3.63 ± 0.56) and SGR (3.63% ± 0.44) compared with the pure breeds, A. percula (3.12 ± 0.42; 2.80% ± 0.42) and A. ocellaris (3.17 ± 0.43; 3.02% ± 0.19). An exponential relationship was found between FCR and SGR in both the breeds. Image analysis displayed a better colour performance of hybrid than the pure breeds. Individual body parts of the hybrid and pure breeds showed significant colour variation between each other. However, colour contrast of whole body of hybrid was found closer to A. ocellaris in hue cone and towards A. percula in saturation and brightness values. Hence, hybrid displays combination colour reflexion of both the parents. The total pigment content of hybrid (65.71 μg g^?1 ± 2.81) was found higher than A. ocellaris (62.01 μg g^?1 ± 2.29) and A. percula (56.71 μg g^?1 ± 2.56). Further, the spectroflurometric analysis revealed that the both hybrid and pure breeds having poor fluorescence on skin pigmentation. A direct positive heterosis was observed on the SGR, FCR, total pigment and spawning frequency, while negative effect was noted on total length of newly hatched larvae (TL), fertilization rate (FrR), hatching rate (HR), deformation rate (DFR) and survival rate (SR). Hence, multiple cross‐breeding programmes will help in developing high‐quality traits in successive generations.     

Effect of electrical stunning at slaughter on the quality of farmed turbot (Psetta maxima)

Food quality aspects of farmed turbot (Psetta maxima) were compared following two methods of slaughter: the current commercial method, by immersion in an ice slurry, which is then dewatered after approximately 20 min, or by first humanely, electrically stunning the fish using a prototype commercial stunner, before immersion in an ice slurry, which is dewatered after 20 min. Quality was assessed for up to 10 days of storage on ice following slaughter. No differences were found between the slaughter methods in terms of an overall carcass quality: overall appearance, haemorrhage, damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. No detectable difference was found between the treatments using the industry standard freshness scoring system, the Quality Index Method. Both groups of fish were classified as ‘Fresh’ after 10 days of storage on ice. Using objective measurements of colour, no differences between fish from either treatment were found in fillet colour. Changes in flesh pH were similar in electrically stunned and traditionally killed fish with a mean pH (±SE) at 2 h post‐mortem of 6.80±0.027 declining to 6.44±0.032 at 24 h post‐mortem. Humane electrical stunning of turbot at slaughter neither detectably improved nor decreased product quality as measured between 1 and 10 days of storage on ice.     

Surplus spermine does not protect salmon cells against lipopolysaccharide (LPS)‐induced stress,but excess spermine is eliminated through spermidine/spermine N1‐acetyltransferase (SSAT)

The present trials tested the efficiency of surplus spermine to reduce inflammation and oxidative stress following LPS‐induced stress using an in vitro model of head kidney and liver cells isolated from Atlantic salmon. Spermine did not protect cells from LPS‐induced inflammatory response at either 0.3, 0.6 or 0.9 mM. However, as the gene expression of spermidine/spermine N1‐acetyltransferase (SSAT) increased with increasing spermine concentration, we addressed possible oxidative effects of the increased SSAT using its activator DENSPM or inhibitor of polyamine oxidation of the acetylated polyamines using MDL72527 at a spermine concentration of 0.6 mM. There was no significant effect of DENSPM, but MDL72527 decreased gene expression of GPX‐3 (p = .04), while gene expression of catalase and MnSOD was unaffected by treatment (p = .30 and p = .48, respectively). In conclusion, spermine did not protect cells from LPS‐provoked inflammation. The higher the spermine concentration, the more SSAT producing acetylated spermine occurred. Inhibiting the acetylated polyamine oxidases by MDL72527 improved oxidation status as expected due to a lower endogenous production of H₂O₂ by polyamine and acetylated polyamine oxidases. Probably care should be taken using polyamines or arginine as functional ingredients to avoid any increased oxidation within cells.     

Effect of electrical stunning at slaughter on the carcass, flesh and eating quality of farmed sea bass (Dicentrarchus labrax)

Food quality aspects of farmed sea bass (Dicentrarchus labrax) were compared following two methods of slaughter: the normal commercial method of killing, by immersion in an ice slurry, or by first electrically stunning the fish, before immersion in an ice slurry. Quality was assessed for up to 10 days of storage on ice after slaughter. No differences were found between the slaughter methods in terms of an overall sensory evaluation of cooked fillets, or in terms of overall carcass quality: overall appearance, internal and external haemorrhage, fin damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. Using objective measurements of colour, no differences between fish from either treatment were found in terms of external colour or colour of the fillets. A chemical analysis of flesh nucleotide breakdown products as well as the freshness indicator K_i value did not differentiate the two treatments nor did the industry standard freshness scoring technique (QIM, quality index method), over 10 days of storage on ice. Flesh pH was marginally lower in electrically stunned fish at 4 h post mortem (6.42 cf 6.56) but by 24 h, pH in fish from both treatments had decreased to a similar level (6.22). Humane electrical stunning of sea bass at slaughter neither measurably improved nor decreased product quality for between 1 and 10 days of storage on ice. Electrical stunning accelerated the pattern of onset and resolution of rigor mortis. If electrical stunning were to be widely adopted, re‐education of buyers would be necessary as rigor mortis is currently used by buyers as a proxy measure of fish freshness.     

Effectiveness of Synthetic Molecules,and Animal and Vegetable Extracts as Baits for Harvesting Red Swamp Crayfish,Procambarus clarkii

Abstract

The present study was designed to evaluate the efficiency of different biogenic amines (putrescine, cadaverine, tyramine, spermine and spermidine) and their precursory amino acids (arginine, histidine, lysine and tyrosine), as well as animal extracts (from fish, crustaceans and mollusks) and vegetable extracts (Chara sp., coconut and alfalfa) as baits in traps for red swamp crayfish, P. clarkii. The methodology was conceived as a logical sequence to proceed from rapid screening of a large number of treatments and was divided into three phases: (1) chemo-detection bioassays, (2) chemattraction bioassays, and (3) field bioassays carried out under natural conditions. The attractants that showed the best performance as baits for P. clarkii, were: the fish soluble extract (included at 2.96%), the putrescine (included at 0.30%) and the red crab soluble extract (included at 2.69%). The benefits of using these attractants, when added to common pelleted feed, come from their low cost, availability and enhanced handling properties.     

Effect of microalgal biomass concentration and temperature on ornamental goldfish (Carassius auratus) skin pigmentation

The aim of this work was to investigate the effect of different carotenoid sources/concentrations and temperature on goldfish (Carassius auratus) skin pigmentation. In the first trial (trial A), the effect of carotenoid source (natural – microalgae Chlorella vulgaris and synthetic – Carophyll Pink) and carotenoid concentration (45, 80 and 120 mg pigment kg^?1 diet) was tested. Six homogeneous duplicate groups of juvenile goldfish (7.4 g) were fed, for 5 weeks, one of the diets containing 45, 80 or 120 mg of total pigments of C. vulgaris biomass or synthetic astaxanthin per kg of diet (Cv45, Cv80, Cv120, Ax45, Ax80, Ax120), respectively. In trial B, the effect of water temperature on skin pigmentation was studied. Five homogeneous duplicate groups of 25 goldfish each (5.2 g) were fed diet Ax45 over 9 weeks, to test the following temperatures: 22, 24, 26, 28 and 30 °C. At the end of both trials, samples of skin along the dorsal fin were withdrawn for subsequent analysis of total carotenoid content, intensity of colour, red and yellow hue and visual observation. The best carotenoid concentrations were achieved with astaxanthin diets. There was a tendency to an overall improvement of colour parameters (L and b) in fish fed diets with high levels of C. vulgaris. The results indicated that the best temperature range to maximize skin pigmentation was 26–30 °C.     

The effect of different carotenoid sources on skin coloration of cultured red porgy (Pagrus pagrus)

This study presents data on the effect of carotenoid sources on skin coloration of red porgy (Pagrus pagrus). Three experiments were conducted: in the first, fish were fed an astaxanthin (Naturose^®)‐supplemented diet, while the second fish received diets supplemented with β‐carotene (Rovimix β‐caroten^®) or lycopene (Lyc‐O‐Mato^®): Carotenoids were added to the level of 100 ppm in each diet, while a non‐carotenoid‐supplemented diet served as a control. In the third experiment, the effect of dietary protein/carbohydrate ratio on melanin content in the skin was investigated. For this experimentation, four diets were formulated to contain 50/23, 40/32, 30/48 and 20/59 protein/carbohydrate ratio. Naturose^® astaxanthin increased total carotenoid content in the dorsal skin area while β‐carotene and lycopene seem to have had no significant effect. Naturose^® was the only carotenoid source that had a significant effect on skin hue, promoting a reddish coloration to the dorsal skin area and a ventral hue similar to wild red porgy. No apparent effect of carotenoid source on skin melanin content was observed. In contrast, dietary protein/carbohydrate ratio affected melanin content in the skin. The fish fed the 50/23 diet showed significantly higher values. Farmed red porgy had eight times higher dorsal‐skin melanin content than wild ones.     

Physicochemical and Microbiological Changes During Drying of Wolf Herring (Chirocentrus dorab) and Coastal Trevally (Carangoides coeruleopinnatus)

The aim of the present study was to assess the physicochemical and microbiological changes during sun drying of salted wolf herring (Chirocentrus dorab) and coastal trevally (Carangoides coeruleopinnatus). For that purpose, the pH value, moisture, sodium chloride (NaCl) content, total volatile base nitrogen (TVB-N), histamine, cadaverine, putrescine, tryptamine, tyramine, spermine, and spermidine, as well as total aerobic mesophilic count, amine forming bacteria, total coliforms, Staphylococcus spp., and Bacillus spp., were determined. The initial pH value was 6.4 and increased during the salt drying process to 6.9 in both cases. The initial moisture, salt, and TVB-N levels of C. dorab and C. coeruleopinnatus were 64.3 and 60.3%, 2.55 and 2.70%, and 22.8 and 16.2 mg/100 g, respectively. At the end of drying, moisture decreased to 31.3 and 35.6%, respectively; salt increased to 13.71 and 16.04%; and TVB-N increased to 35.9 and 33.13 mg/100 g, respectively. Regarding total aerobic mesophilic count, amine forming bacteria, total coliforms, Staphylococcus spp., and Bacillus spp., a statistically significant (P < 0.05) reduction of the population was observed in both cases. Regarding the biogenic amine forming bacteria, Morganella morganii and Klebsiella pneumoniae were isolated from C. dorab; Bacillus cereus, Staphylococcus xylosus, and Providencia rettgeri were isolated from C. coeruleopinnatus. During sun drying, the amount of histamine, cadaverine, putrescine, and tryptamine was reduced; spermine was detected in C. dorab only during the first day, whereas spermidine was not detected. This reduction may be attributed to the presence of biogenic amine decomposing bacteria. However, further research is necessary in order to verify in situ this capacity and exploit potential applications for fish and fishery products.     

The effect of dietary vitamin E and C level on market-size turbot (Scophthalmus maximus) fillet quality

Fish fillet quality has been shown to be influenced by the level of antioxidants in preslaughter diet. Thus, an experiment was conducted to study the effect of different levels of vitamin E and C on the fillet quality of market‐size reared turbot (Scophthalmus maximus). Turbot of a mean initial weight of 347 ± 20 g were divided into four groups and fed commercial turbot diets (60% protein, 12% fat), supplemented with α‐tocopheryl acetate (mg kg^?1) and ascorbyl‐2 monophosphate (mg kg^?1) at the following dietary levels: 500/100, 1000/100, 100/1000, 100/100 respectively. Over a dietary supplementation period of 15 weeks, fish were fed to satiation and reached a final mean weight of 916 ± 29 g. α‐Tocopherol levels increased significantly (P < 0.001) in tissue (i.e. muscle, liver, heart and kidney) of fish fed diets containing elevated levels of α‐tocopheryl acetate. In ice storage, fillets of these fish exhibited significantly lower (P < 0.001) levels of lipid oxidation, and showed significantly less (P < 0.001) colour deterioration (higher hue angle and lower chroma). Elevated dietary α‐tocopheryl acetate levels had a negative effect (P ≤ 0.001) on the concentration of ascorbic acid in muscle tissue. An increase in dietary vitamin C did not have any detectable effect on fillet quality. Prolonged feeding times had a negative effect on lipid oxidation (P < 0.001) and colour deterioration (P < 0.01). These results suggest that increased dietary α‐tocopheryl acetate could prevent colour deterioration and lipid oxidation of turbot fillets in retail storage on ice.     

Effect of carotenoids on body colour of discus fish (Symphysodon aequifasciatus axelrodi Schultz, 1960)

This study assessed the effects of three kinds of carotenoids on the body colour of solid red discus fish (Symphysodon aequifasciatus axelrodi Schultz, 1960). Astaxanthin, xanthophylls and canthaxanthin were added into the beef heart diet at the level of 350 mg kg^?1 respectively. In the astaxanthin group (group A), the carotenoid concentration (CC) in the skin and dorsal fin reached saturation levels on days 40 and 20 respectively. However, CC consistently increased in the muscle. In the xanthophyll group (group B), CC in the skin increased through day 20; CC in the dorsal fin increased from days 10 to 20. In the canthaxanthin group (group C), CC in the skin increased during the first 20 days, reaching saturation levels on day 10 in the dorsal fin and muscle. On day 50, CC in the skin and muscle of group A was significantly higher than that of groups B or C. There were no significant differences in dorsal fin CC among the groups; however, CC in group C reached saturation levels in the shortest time. Therefore, astaxanthin was the most effective pigment for the skin and muscle; xanthophyll was the most effective pigment for the dorsal fin.     

乌鳢抽出物成分的研究

分析了乌鳢(Channaargus)即杀后背肉、腹肉、尾部肉、肝脏、生殖腺中ATP关联化合物、游离氨基酸、多胺、糖元及糖酵解中间代谢物、有机酸等的含量。ATP关联化合物在肌肉中的总量为7.5～8.0μmol·g-1。ATP在背肉含量为3.9μmol·g-1,腹肉为4.1μmol·g-1,尾部肉为4.7μmol·g-1。运动激烈的尾部肉ATP占63%,含量相当高。肝脏中有少量的腺苷与肌苷酸一起被检出,据此可认为ATP的分解存在两个途径。游离氨基酸总量在背肉中为436.0mg·(100g)-1,腹肉中为405.0mg·(100g)-1,尾部肉中为356.3mg·(100g)-1。牛磺酸和甘氨酸为主要氨基酸,占68%～73%。丙氨酸和谷氨酸也相当高的含量检出。肌肉中的多胺检出为精胺和亚精胺,肝脏和生殖腺中有较高浓度的腐胺及亚精胺和精胺检出。即杀后糖元的量约占肌肉的0.5%,还有相当多的葡萄糖和6磷酸葡萄糖的糖酵解中间代谢物以及其最终产物乳酸的大量检出。     

Colour measurement, using the CIELCH colour space, of muscle of rainbow trout, Oncorhynchus mykiss (Walbaum), fed astaxanthin: effects of family, ploidy, sex, and location of reading

Thirty two families (representing 397 fish of 900 g average weight) of rainbow trout. Oncorhynchus mykiss (Walbaum) (16 diploid sib-groups and their homologous triploids obtained by heat shock) were fed astaxanthin (96 mg kg^-1 feed) for 39 days, resulting in a red colouring of the muscle. The colour was measured in the CIELCH colour space using a chromameter at three points of fish muscle (head, middle and tail). The effects of ploidy, sex, family and location of measurement on the colour attributes offish muscle (lightness, chroma and hue angle) were analysed. Diploid fish had a higher chroma than triploid ones (P<0.02), but no ploidy effect was found on lightness nor on hue angle. Sex had little influence on colour attributes, except for the hue angle which was slightly higher (P<0.07) in females than in males. Family had a strong effect on chroma (P<0.002), hue angle (P<0.02), and, to a lesser extent, on lightness (P<0.07). However, within families the muscle colour was very variable from one fish to another (highly significant variation [P<0.0001] on every colour attribute). The location effect was highly significant on lightness (P<0.0001), chroma (P<0.0001), and hue angle (P<0.0001). Data from the tail part of the fish muscle were higher than those from the head part. The middle part always exhibited the lowest data.     

Effect of Antarctic krillmeal on quality of farmed Atlantic cod (Gadus morhua L.)

Farmed Atlantic cod with a mean weight of 4.8 kg were maintained for 9 weeks in sea cages and fed diets where the dietary fishmeal component was substituted with increasing proportions (0%, 22%, 63% and 100%) of meal from Antarctic krill, Euphausia superba. Wild‐caught cod were included in the study as external control. At termination of feeding, all fish were slaughtered and muscle pH was immediately recorded. The fish were then stored on ice for three days and assessed for muscle pH and objective (skin and fillet colour, and fillet texture) and subjective (sensory evaluation) quality criteria. Replacement of fishmeal with krillmeal in the diets resulted in the skin colour above and below the lateral line to be more red than the control group without krillmeal substitutions, even though this difference was not significant, and with more yellow hue. Additions of krillmeal increased the muscle whiteness and yellow hue compared with the control group and wild fish. There was no difference in red hue between the groups. Muscle pH, texture or sensory attributes were unaffected by dietary inclusion level of krillmeal. Wild‐caught cod deviated in several aspects from the farmed cod. It is concluded that the replacement of fishmeal with Antarctic krillmeal in the diets two months before slaughter did not move the sensory attributes more towards wild fish.     

Effect of cage colour and light environment on the skin colour of Australian snapper Pagrus auratus (Bloch & Schneider, 1801)

A two‐factor experiment was performed to evaluate the effects of cage colour (black or white 0.5 m³ experiment cages) and light environment (natural sunlight or reduced level of natural sunlight) on the skin colour of darkened Australian snapper. Each treatment was replicated four times and each replicate cage was stocked with five snapper (mean weight=351 g). Snapper exposed to natural sunlight were held in experimental cages located in outdoor tanks. An approximately 70% reduction in natural sunlight (measured as PAR) was established by holding snapper in experimental cages that were housed inside a ‘shade‐house’ enclosure. The skin colour of anaesthetized fish was measured at stocking and after a 2‐, 7‐ and 14‐day exposure using a digital chroma‐meter (Minolta CR‐10) that quantified skin colour according to the L^*a^*b^* colour space. At the conclusion of the experiment, fish were killed in salt water ice slurry and post‐mortem skin colour was quantified after 0.75, 6 and 22 h respectively. In addition to these trials, an ad hoc market appraisal of chilled snapper (mean weight=409 g) that had been held in either white or in black cages was conducted at two local fish markets. Irrespective of the sampling time, skin lightness (L^*) was significantly affected by cage colour (P<0.05), with fish in white cages having much higher L^* values (L^*≈64) than fish held in black cages (L^*≈49). However, the value of L^* was not significantly affected by the light environment or the interaction between cage colour and the light environment. In general, the L^* values of anaesthetized snapper were sustained post mortem, but there were linear reductions in the a^* (red) and b^* (yellow) skin colour values of chilled snapper over time. According to the commercial buyers interviewed, chilled snapper that had been reared for a short period of time in white cages could demand a premium of 10–50% above the prices paid for similar‐sized snapper reared in black cages. Our results demonstrate that short‐term use of white cages can reduce the dark skin colour of farmed snapper, potentially improving the profitability of snapper farming.